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[vsnet-grb-info 42639] SVOM GRB 260509A: MASTER-OAFA optical observation
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44512 SUBJECT: SVOM GRB 260509A: MASTER-OAFA optical observation DATE: 26/05/10 08:23:16 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> Ya.Kechin (Lomonosov MSU), F.Podesta, M.J. Segura, C.Francile, R.Podesta, E. Gonzalez (OAFA, SJNU), A.Kuznetsov, V.Lipunov, I.Panchenko, P.Balanutsa, G.Antipov, N.Tiurina,K.Zhirkov, E.Gorbovskoy, V.Senik, A.Chasovnikov, V.Topolev, D.Vlasenko,A.Sankovich, I.Gorbunov(Lomonosov MSU), N.Budnev, O.Gress (ISU), D.Buckley (SAAO), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A. Gabovich (Blagoveschensk Educational StateUniversity) R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez,J.Martinez,A.R.Corella, J.Tanori, L. Villalobos, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope of MASTER Global Robotic Net [1-4] was pointed to the SVOM GRB260509A (trigger No 1778363469,11h 47m 32.88s , +00d 12m 34.2s, R=0.0786667 Gotz et al. GCN 44504) errorbox 8054 sec after notice time and 10202 sec after trigger time at 2026-05-10 00:41:11 UT, with upper limit up to 20.5 mag. The observations began at zenith distance = 31 deg. The sun altitude is -36.5 deg. MASTER-OAGH robotic telescope located in Mexico (OAGH National Institute for Astrophysics, Optics and Electronics) was pointed to the SVOM GRB260509.91 errorbox 24424 sec after notice time (26572 sec after trigger time at 2026-05-10 05:14:01 UT), with upper limit up to 19.3 mag. The observations began at zenith distance = 36 deg. The sun altitude is -33.4 deg. The galactic latitude b = 59 deg., longitude l = 272 deg. There is MASTER OT J114735.9135.91+001717.7 optical counterpart at first images with m_OT~20.9 at 2026-05-10 00:41:11UT discovered by GOTO (O'Neill et al. GCN 44505) and observed by LCO (Saccardi et al. GCN 44506), SVOM|VT (Wu et al. GCN 44507), KAIT (Zheng et al. GCN 44510) Real time updated cover map and OT are available here: https://master.sai.msu.ru/site/master2/observ.php?id=3303991 MASTER upper limits: Tmid-T0 | Date Time | Site | Coord J2000) |Filt.| Expt. | Limit| Comment 10233 | 2026-05-10 00:41:11 | MASTER-OAFA | (11h 44m 48.88s , -00d 51m 54.0s) | C | 60 | 20.2 | 10293 | 2026-05-10 00:41:11 | MASTER-OAFA | (11h 44m 48.87s , -00d 51m 54.0s) | C | 180 | 20.5 | Coadd 10311 | 2026-05-10 00:42:29 | MASTER-OAFA | (11h 44m 48.21s , -00d 50m 56.7s) | C | 60 | 20.2 | 10389 | 2026-05-10 00:43:47 | MASTER-OAFA | (11h 44m 52.24s , -00d 51m 59.4s) | C | 60 | 20.2 | 10465 | 2026-05-10 00:45:03 | MASTER-OAFA | (11h 44m 46.21s , -00d 53m 02.8s) | C | 60 | 20.2 | 10525 | 2026-05-10 00:45:03 | MASTER-OAFA | (11h 44m 46.20s , -00d 53m 02.8s) | C | 180 | 20.5 | Coadd 10540 | 2026-05-10 00:46:19 | MASTER-OAFA | (11h 44m 52.06s , -00d 52m 51.7s) | C | 60 | 20.2 | 10618 | 2026-05-10 00:47:36 | MASTER-OAFA | (11h 44m 49.58s , -00d 51m 21.4s) | C | 60 | 20.2 | 10697 | 2026-05-10 00:48:55 | MASTER-OAFA | (11h 44m 49.29s , -00d 53m 05.6s) | C | 60 | 20.2 | 10757 | 2026-05-10 00:48:55 | MASTER-OAFA | (11h 44m 49.28s , -00d 53m 05.6s) | C | 180 | 20.4 | Coadd 10774 | 2026-05-10 00:50:12 | MASTER-OAFA | (11h 44m 52.95s , -00d 51m 27.6s) | C | 60 | 20.2 | 10852 | 2026-05-10 00:51:31 | MASTER-OAFA | (11h 44m 45.40s , -00d 52m 20.8s) | C | 60 | 20.2 | 10930 | 2026-05-10 00:52:48 | MASTER-OAFA | (11h 44m 45.82s , -00d 51m 24.8s) | C | 60 | 20.2 | 10990 | 2026-05-10 00:52:48 | MASTER-OAFA | (11h 44m 45.81s , -00d 51m 24.8s) | C | 180 | 20.4 | Coadd 11007 | 2026-05-10 00:54:06 | MASTER-OAFA | (11h 44m 49.85s , -00d 52m 28.2s) | C | 60 | 20.2 | 11086 | 2026-05-10 00:55:24 | MASTER-OAFA | (11h 44m 45.55s , -00d 53m 32.1s) | C | 60 | 20.2 | 11160 | 2026-05-10 00:56:39 | MASTER-OAFA | (11h 44m 49.59s , -00d 53m 31.6s) | C | 60 | 20.2 | 11220 | 2026-05-10 00:56:39 | MASTER-OAFA | (11h 44m 49.59s , -00d 53m 31.6s) | C | 180 | 20.4 | Coadd [1] Lipunov et al., 2010, Advances in Astronomy, vol. 2010, 30L [2] Lipunov et al. 2022, Universe, Vol. 8(5), id.271 [3] Lipunov et a. 2019, ARep, vol.63, 293 [4] Lipunov et al. 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics,Lomonosov MSU PRESS, 591pp. http://www.pereplet.ru/lipunov/625.html#625 View this GCN Circular online at https://gcn.nasa.gov/circulars/44512. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42638] Fermi GRB 260510A: Global MASTER-Net observations report
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44511 SUBJECT: Fermi GRB 260510A: Global MASTER-Net observations report DATE: 26/05/10 06:30:25 GMT FROM: Vladimir Lipunov at Moscow State U/Krylov Obs <lipunov(a)xray.sai.msu.ru> V.Lipunov, E.Gorbovskoy, A.Kuznetsov, K.Zhirkov, I.Panchenko, N.Tiurina, P.Balanutsa, V.Topolev, D.Vlasenko, G.Antipov, A.Sankovich, Yu.Tselik, Ya.Kechin, V.Senik, A.Chasovnikov, K.Labsina, I. Gorbunov (Lomonosov MSU), O.Gress, N.Budnev (ISU), C.Francile, F. Podesta, R.Podesta, E. Gonzalez (Observatorio Astronomico Felix Aguilar (OAFA), A. Tlatov, D. Dormidontov (Kislovodsk Solar Station of the Pulkovo Observatory), A.Sosnovskij (CrAO), A. Gabovich, V.Yurkov (Blagoveschensk Educational StateUniversity), D.Buckley (SAAO), R.Rebolo (The Instituto de Astrofisica de Canarias), L.Carrasco, J.R.Valdes, V.Chavushyan, V.M.Patino Alvarez, J.Martinez, A.R.Corella, L.H.Rodriguez (INAOE, Guillermo Haro Astrophysics Observatory) MASTER-OAFA robotic telescope [1] located in Argentina (OAFA observatory of San Juan National University) started inspect of the Fermi GRB 260510A ( Fermi GBM team, GCN 44508) errorbox 12795 sec after notice time and 12848 sec after trigger time at 2026-05-10 06:20:28 UT, with upper limit up to 17.6 mag. The observations began at zenith distance = 80 deg. The sun altitude is -61.8 deg. The galactic latitude b = -73 deg., longitude l = 333 deg. Real time updated cover map and OT discovered available here: https://master.sai.msu.ru/site/master2/observ.php?id=3304437 We obtain a following upper limits. Tmid-T0 | Date Time | Site | Coord (J2000) |Filt.| Expt. | Limit| Comment _________|_____________________|_____________________|____________________________________|_____|_______|_______|________ 12879 | 2026-05-10 06:20:28 | MASTER-OAFA | (00h 01m 07.12s , -42d 06m 59.6s) | C | 60 | 17.0 | 12956 | 2026-05-10 06:21:45 | MASTER-OAFA | (00h 01m 04.44s , -42d 05m 38.2s) | C | 60 | 16.9 | 13034 | 2026-05-10 06:23:03 | MASTER-OAFA | (00h 01m 02.62s , -44d 07m 12.4s) | C | 60 | 17.4 | 13109 | 2026-05-10 06:24:18 | MASTER-OAFA | (00h 01m 04.74s , -44d 05m 38.9s) | C | 60 | 17.5 | 13186 | 2026-05-10 06:25:35 | MASTER-OAFA | (00h 00m 59.38s , -44d 06m 16.7s) | C | 60 | 17.6 | Filter C is a clear (unfiltred) band. The observation and reduction will continue. The message may be cited. [1] - V.M. Lipunov, V.G. Kornilov, E.S. Gorbovskoy, N.A. Tiurina & A.S.Kuznetsov, 2023, Astronomical Robotic Networks and Operative Multichanel Astrophysics, Lomonosov MSU PRESS, 591pp. http : // www.pereplet.ru/lipunov/625.html View this GCN Circular online at https://gcn.nasa.gov/circulars/44511. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42637] GRB 260509A: KAIT optical observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44510 SUBJECT: GRB 260509A: KAIT optical observations DATE: 26/05/10 06:13:38 GMT FROM: Weikang Zheng at UC Berkeley <weikang(a)berkeley.edu> WeiKang Zheng (UCB), Xuhui Han (NAOC), Pinpin Zhang (NAOC) and Alexei V. Filippenko (UCB) report on behalf of the KAIT GRB team: The 0.76-m Katzman Automatic Imaging Telescope (KAIT), located at Lick Observatory, observed the field of GRB 260509A (Götz et al., GCN 44504 starting at 04:56 UT, 7.08 hours after the burst. A set of clear (roughly R) filter images were obtained. We detected the afterglow (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506; Wu et al., GCN 44507; Álvarez et al., GCN 44509) in our coadd image. We measure its brightness to be 21.1 +/- 0.2 mag (Vega) at mid time of 7.37 hours after the burst. View this GCN Circular online at https://gcn.nasa.gov/circulars/44510. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42636] GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44509 SUBJECT: GRB 260509A: SVOM/COLIBRÍ (FM-GFT) observations DATE: 26/05/10 04:54:27 GMT FROM: freddalvarez(a)astro.unam.mx Fredd Sánchez Álvarez (UNAM), Jean-Grégoire Ducoin (CPPM), Alan M. Watson (UNAM), Stéphane Basa (UAR Pytheas), William H. Lee (UNAM), Edilberto Aguilar-Ruiz (UNAM), Jean-Luc Atteia (IRAP), Camila Angulo (UNAM), Dalya Akl (NYUAD), Sarah Antier (IJCLAB), Rosa L. Becerra (UNAM), Nathaniel R. Butler (ASU), Damien Dornic (CPPM), Francis Fortin (IRAP), Leonardo García García (UNAM), Ramandeep Gill (UNAM), Noémie Globus (UNAM), Marion Guelfand (CPPM), Asuka Kuwata (UNAM), Massimiliano Lincetto (CPPM), Diego López-Cámara (UNAM), Francesco Magnani (CPPM),Nikos Mandarakas (LAM), Enrique Moreno Méndez (UNAM), Margarita Pereyra (UNAM), Ny Avo Rakotondrainibe (LAM), Benjamin Schneider (LAM), Antonio de Ugarte Postigo (LAM), and D. Adrien (CEA/Irfu) report: We imaged the field of the SVOM/ECLAIRs GRB 260509A (Götz et al. GCN 44504) using the DDRAGO two-channel wide-field imager on the COLIBRÍ telescope. We observed from 2026-05-10 03:31 to 03:59 UTC and obtained 8 minutes of exposure in g, r, and i, and simultaneously 24 minutes of exposure in z. The data were reduced, coadded, calibrated, and analyzed with the COLIBRÍ ASU pipeline. The photometry was calibrated using nearby stars from the PanSTARRS DR1 catalog, is in the AB system, and is not corrected for Galactic extinction. We detect the optical counterpart reported by O’Neill et al.(GCN 44505), Saccardi et al. (GCN 44506), and Wu et al. (GCN 44507) with preliminary magnitudes of: g = 21.25 +/- 0.05 r = 21.31 +/- 0.08 i = 20.97 +/- 0.08 z = 20.81 +/- 0.09 Our strong detection of the source in g suggests that the redshift is less than 3.0. We thank the staff of the Observatorio Astronómico Nacional at Sierra de San Pedro Mártir, as well as the technical and engineering teams at CEA, CPPM, IRAP, LAM, OHP, OSU Pytheas, and UNAM. COLIBRÍ is an astronomical observatory developed and operated jointly by France (AMU, CNES and CNRS) and Mexico (UNAM and SECIHTI). It is located at the Observatorio Astronómico Nacional on the Sierra de San Pedro Mártir, Baja California, Mexico. View this GCN Circular online at https://gcn.nasa.gov/circulars/44509. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42635] GRB 260510A: Fermi GBM Final Real-time Localization
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44508 SUBJECT: GRB 260510A: Fermi GBM Final Real-time Localization DATE: 26/05/10 02:57:06 GMT FROM: Fermi GBM Team at MSFC/Fermi-GBM <do_not_reply(a)GIOC.nsstc.nasa.gov> The Fermi GBM team reports the detection of a likely LONG GRB At 02:46:19 UT on 10 May 2026, the Fermi Gamma-ray Burst Monitor (GBM) triggered and located GRB 260510A (trigger 800073984.34868 / 260510115). The on-ground calculated location, using the Fermi GBM trigger data, is RA = 0.5, Dec = -41.9 (J2000 degrees, equivalent to J2000 00h 02m, -41d 53'), with a statistical uncertainty of 6.1 degrees. The angle from the Fermi LAT boresight is 84.0 degrees. The skymap can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… The HEALPix FITS file, including the estimated localization systematic, can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… The GBM light curve can be found here: https://heasarc.gsfc.nasa.gov/FTP/fermi/data/gbm/triggers/2026/bn260510115/… View this GCN Circular online at https://gcn.nasa.gov/circulars/44508. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42634] GRB 260509A: SVOM/VT optical candidate with VHF data
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44507 SUBJECT: GRB 260509A: SVOM/VT optical candidate with VHF data DATE: 26/05/10 01:47:02 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> C. Wu, H. L. Li, Y. L. Qiu, L. P. Xin (NAOC), J. T. Palmerio (CEA/Irfu), D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU) on behalf of the SVOM/VT team. After the trigger by SVOM/ECLAIRs (SVOM burst-id sb26050905) at 2026-05-09T21:51:09 UTC (T0), SVOM/VT began observing the field after the automatic slew on the burst (Götz et al., GCN 44504) in the VT_B (400nm-650nm) and VT_R (650nm-1000nm) channels simultaneously. From a preliminary analysis of the 1-bit subimage and source list generated by on-board data processing and downloaded via VHF network, one credible candidate is identified, the details of which are presented below. VT_ID 722: The position of this candidate is R.A., Dec. 176.8997, 0.2882 degrees, corresponding to: R.A. (J2000) = 11:47:35.9 Dec. (J2000) = 00:17:17.6 with an uncertainty of 0.50 arcsec. This candidate was detected in both VT_R and VT_B, and was flagged as an uncatalogued source whose brightness faded during the VT observations. The candidate's magnitudes are: | date-obs (UTC) | mid-time | exposure | VT_B mag(AB) | VT_R mag(AB) | | -------------------- | ----------- | --------- | ------------- | ------------- | | 2026-05-09T23:18:31 | 89.87 min | 6x50 sec | 20.38 ± 0.03 | 19.80 ± 0.04 | | 2026-05-09T23:58:59 | 129.08 min | 3x50 sec | 20.67 ± 0.05 | 20.18 ± 0.06 | Magnitudes were not corrected for Galactic extinction. The mean color of VT_B - VT_R = 0.54 is in line with the expectations of an event at redshift z < 4. The position of this candidate is consisent with the reports (O'Neill et al., GCN 44505; Saccardi et al., GCN 44506) . The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/VT was jointly developed by Xi'an Institute of Optics and Precision Mechanics (XIOPM), CAS and National astronomical observatories (NAOC), CAS. View this GCN Circular online at https://gcn.nasa.gov/circulars/44507. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42633] GRB 260509A: LCO optical counterpart detection
by GCN Circulars 10 May '26

10 May '26

TITLE: GCN CIRCULAR NUMBER: 44506 SUBJECT: GRB 260509A: LCO optical counterpart detection DATE: 26/05/10 01:00:45 GMT FROM: SVOM_group <svomgroup(a)bao.ac.cn> A. Saccardi (CEA/Irfu), C. Wu (NAOC), D. Adrien (CEA/Irfu), L. Zhang (IHEP), Y. H. Cheng (YNU), report on behalf of the SVOM mission team: We observed the field of GRB 260509A detected by SVOM (Götz et al., GCN 44504) with the LCO 1m telescope at Cerro Tololo Observatory equipped with the Sinistro instrument. Our observation started on 2026-05-09 at 23:41:26 UT (about 1.84 hr after the trigger) and we obtained 3x200 s exposures in the SDSS r and 3x200 s exposures in the Pan-STARRS z filters. The optical candidate reported by O'Neill et al. (GCN 44505) is clearly detected in our images. We measure the following magnitudes calibrated against the Pan-STARRS DR1 catalog, and not corrected for Galactic extinction: r = 19.79 +/- 0.05 AB (mid-time 1.92 hr after the trigger); z = 19.76 +/- 0.15 AB (mid-time 2.65 hr after the trigger). This project is funded by the SVOM collaboration. View this GCN Circular online at https://gcn.nasa.gov/circulars/44506. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42632] GRB 260509A: GOTO optical counterpart candidate
by GCN Circulars 09 May '26

09 May '26

TITLE: GCN CIRCULAR NUMBER: 44505 SUBJECT: GRB 260509A: GOTO optical counterpart candidate DATE: 26/05/09 23:23:47 GMT FROM: Sergey Belkin at Monash University <sergey.belkin(a)monash.edu> D. O'Neill, S. Belkin, K. Ulaczyk, A. Kumar, K. Ackley, M. Dyer, J. Lyman, D. Steeghs, D. Galloway, V. Dhillon, P. O'Brien, G. Ramsay, K. Noysena, R. Kotak, R. Breton, J. Casares, L. Nuttall, R. Starling, B. Gompertz, B. Godson, T. Killestein, M. Pursiainen, on behalf of GOTO collaboration. We report on optical observations with the Gravitational-wave Optical Transient Observer (GOTO; Steeghs et al. 2022, Dyer et al. 2024) in response to the SVOM/ECLAIRS alert GRB 260509A (sb26050905, Götz et al. GCN 44504). Observations covering the localisation area were taken at 2026-05-09 21:56:19 UT, (t0 +0.09h) with an average 5-sigma depth of 20.8 mag. Images were processed immediately after acquisition using the GOTO pipeline. Difference imaging was performed using deeper template observations (Lyman et al. 2026). Source candidates were initially filtered using a classifier (Killestein et al. 2021) and cross-matched against a variety of contextual and minor planet catalogs. Human vetting was carried out in real time on any candidates that passed the above checks. A new optical source GOTO26emi is identified near the edge of the ECLAIRS localisation region, at an angular separation of 4.79 arcmin from the reported GRB position, marginally outside the quoted 4.72 arcmin error radius. The source coordinates: RA,DEC (J2000) = 176.899834, 0.288276, 11:47:35.96, +00:17:17.80 The rapidly rising source was detected with average L = 20.13 ± 0.16 AB mag (+0.09h). We find no evidence of the source prior to the GRB trigger time in previous GOTO observations taken at 2026-05-09 10:38:10 (-11.21h) down to a depth of >20.40 AB mag, the ZTF observations provided by the Lasair broker (Smith et al. 2019), or the ATLAS forced photometry server (Shingles et al. 2021). GOTO (https://goto-observatory.org) is a network of telescopes that is principally funded by the STFC and operated at the Roque de los Muchachos Observatory on La Palma, Spain, and Siding Spring Observatory in NSW, Australia, on behalf of a consortium including the University of Warwick, Monash University, Armagh Observatory & Planetarium, the University of Leicester, the University of Sheffield, the National Astronomical Research Institute of Thailand (NARIT), the University of Turku, the University of Portsmouth, the University of Manchester, the University of Birmingham and the Instituto de Astrofisica de Canarias (IAC). View this GCN Circular online at https://gcn.nasa.gov/circulars/44505. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42631] GRB 260509A: SVOM detection of a burst
by GCN Circulars 09 May '26

09 May '26

TITLE: GCN CIRCULAR NUMBER: 44504 SUBJECT: GRB 260509A: SVOM detection of a burst DATE: 26/05/09 22:26:24 GMT FROM: Diego Gotz at CEA <diego.gotz(a)cea.fr> GRB 260509A: SVOM detection of a burst D. Götz (CEA/Irfu), A. Saccardi (CEA/Irfu), H. Goto (RIKEN), F. Lacreu (IAP), D. Adrien (CEA/Irfu), report on behalf of the SVOM mission team: At 2026-05-09T21:51:09 UTC (T0), SVOM/ECLAIRs triggered and located the gamma-ray burst GRB 260509A (SVOM burst-id sb26050905). The following trigger information was received on the ground with low latency by the SVOM VHF Alert Network. The burst was detected both by the Count-Rate Trigger (CRT) and the Image Trigger (IMT), which produced a sequence of 18 alerts. CRT provided the alert with the best signal-to-noise-ratio in the image (SNR) of 18.00 in the [5-20] keV energy band over a time window of 20.40 seconds starting at 2026-05-09T21:51:03. The localization of the best alert is R.A., Dec. 176.8870, 0.2095 degrees: R.A. (J2000) = 11h47m32.9s Dec. (J2000) = 0d12m34.2s with a 90% confidence level (C.L.) radius of 4.72 arcmin (including systematic error of 2 arcmin added in quadrature). We note the presence of a high proper motion star G 10-49 at a distance of 4.48 arcmin from the ECLAIRs position. The SVOM/ECLAIRs light curve showed a single peak structure with a T90 duration of about 14.7 +/-0.6 s. This burst was also detected by SVOM/GRM with a significance of 6.40. The SVOM/GRM light curve showed a double peak structure with a T90 duration of about 18 (-6/+10) s. SVOM slewed to the burst. MXT and VT began observing the field after the slew. The analysis of the data will be published in future circulars. The Space-based multi-band astronomical Variable Objects Monitor (SVOM) is a China-France joint mission led by the Chinese National Space Administration (CNSA), French Space Agency (CNES), and the Chinese Academy of Sciences (CAS), which is dedicated to observing gamma-ray bursts and other transient phenomena in the energetic universe. SVOM/ECLAIRs was developed jointly by CNES, CEA-IRFU, CNRS-IRAP, CNRS-APC. SVOM/GRM was developed by the Institute of High Energy Physics (IHEP) of CAS. SVOM/MXT was developed jointly by CNES, CEA-IRFU, CNRS-IJCLab, University of Leicester, MPE. The Burst Advocate (BA) on shift for this alert is Dylan Adrien: dylan.adrien(a)cea.fr. Please contact the BA by email if you require additional information. View this GCN Circular online at https://gcn.nasa.gov/circulars/44504. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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[vsnet-grb-info 42630] GRB 260506B: AstroSat CZTI detection
by GCN Circulars 08 May '26

08 May '26

TITLE: GCN CIRCULAR NUMBER: 44503 SUBJECT: GRB 260506B: AstroSat CZTI detection DATE: 26/05/08 19:22:25 GMT FROM: Anuraag Arya at IIT Bombay <aryaanuraag910(a)gmail.com> S. Salunke (IUCAA), Harsha K. H. (IUCAA), M. Tembhurnikar (IUCAA), A. Goyal (IITB), A. Arya (IITB), G. Waratkar (Caltech/IITB), A. Vibhute (IUCAA), V. Bhalerao (IITB), D. Bhattacharya (Ashoka University/IUCAA), A. R. Rao (IUCAA/TIFR), and S. Vadawale (PRL) report on behalf of the AstroSat CZTI collaboration: Analysis of AstroSat CZTI data with the CIFT2 framework showed the detection of GRB 260506B which is also detected by the Fermi/GBM (Fermi GBM team, GCN Circ. 44484). The source was clearly detected in the CZT detectors in the 20-200 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-05-06 13:07:41.9 UTC. The measured peak count rate associated with the burst is 129 (+37, -17) counts/s above the background in the combined data of all four quadrants, with a total of 899 (+239, -328) counts. The local mean background count rate was 289 (+2, -3) counts/s. Using cumulative rates, we measure a T90 of 22 (+12, -15) s. We caution that there is a 0.3 s dead time in the CZTI data in the burst, hence the actual T90 may be slightly longer. The source was also clearly detected in the CsI anticoincidence (Veto) detector in the 100-500 keV energy range. The light curve showed multiple peaks of emission with the strongest peak at 2026-05-06 13:07:42.0 UTC. The measured peak count rate associated with the burst is 440 (+67, -69) counts/s above the background in the combined data of all quadrants, with a total of 3325 (+520, -551) counts. The local mean background count rate was 1313 (+4, -4) counts/s. We measure a T90 of 36 (+3, -7) s from the cumulative Veto light curve. CZTI is built by a TIFR-led consortium of institutes across India, including VSSC, URSC, IUCAA, SAC, and PRL. The Indian Space Research Organisation funded, managed, and facilitated the project. CZTI data products like interactive and downloadable light curves for this GRB can be found at: https://astrosat.iucaa.in/cift/cift_products/515768858.51/S515768858.51_det… CZTI GRB detections are reported regularly on the payload site at: http://astrosat.iucaa.in/czti/?q=grb View this GCN Circular online at https://gcn.nasa.gov/circulars/44503. --- To unsubscribe, open this link in a web browser: https://gcn.nasa.gov/unsubscribe/eyJhbGciOiJIUzI1NiJ9.eyJlbWFpbCI6InZzbmV0L…

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